The present invention relates to borehole logging tools, and in particular to aspects of an actuating mechanism urging a borehole logging tool against the wall of a borehole.
Borehole logging tools are known for performing measurements in boreholes to evaluate surrounding underground formations and often contact between the tool and the borehole is necessary to perform the desired measurement. This contact can be provided by anchoring the tool to a borehole wall during a measurement operation through the use of an anchoring arm. It may be necessary to make measurements at a number of levels in a borehole so the anchoring arm must be released to allow the tool to be moved and the anchoring arm then re-engaged at the next level. The time taken for the anchor to release and to re-engage can be a significant factor in the time taken to make a measurement at each level. An anchor arm that can be anchored and released in a relatively short time is desirable.
For example, multi-shuttle seismic tools are known that comprise a number shuttles linked together by means of a cable and logged through a borehole while seismic signals are generated at the surface. At each measurement level, each shuttle is anchored to the wall of a borehole during a measurement operation by means of an anchoring arm. As the time required to anchor and release each shuttle increases, the cost of performing the measurement operation increases and the possibility of the tool becoming encumbered in the borehole increases. In Schlumberger""s Combinable Seismic Imager tool (CSI) the anchoring arm of each shuttle extended under spring bias and a drive motor is used to provide the anchoring force or retraction. Aspects of the CSI are described in U.S. Pat. Nos. 4,563,757; 4,575,831; 4,987,969; and 5,200,581. In patents ""757 and ""831 relate to the anchoring mechanism and procedure. A schematic figure from the patents is shown in FIG. 1. This prior art arrangement includes a motor 35, an output reducer 36 with an electromagnetic brake 37 and an output shaft to a coupling device 39 comprising a clutch 50, a mechanical logic 51 and torque limiter 54. The mechanical logic 51 includes studs located in helical, V-shaped, cam slots that serve to bring the clutch into engagement on operation of the motor. Drive is transmitted to a push rod 34 connected to the anchoring arms 31, 32 by means of a ball screw 40 and nut 41. The anchoring arms are urged away from the tool body 29 by a leaf spring 43 which is fixed to the tool body 29 and bears upon the arm 31. When in the open position, a pad 30 at the end of the arms 31, 32 engages the borehole wall and causes the tool body 29 to be pushed against the opposite side of the borehole where it can be anchored for use. The motor 35 is used to provide the extra anchoring force to the arms 31,32 and to withdraw the arms when the tool is run in or pulled out of the borehole. When the tool is to be moved to a different level, the action of the clutch 50 allows the motor to be disengaged and the arms held only by the force of the leaf spring 43.
An object of the present invention is a tool which has an anchoring arm which can be anchored and released in a relatively short time, and a further object is a tool which has a relatively compact anchoring arm. Another object is a borehole tool in which measurements relating to the anchoring mechanism or tool body position can be made. A further object is an anchoring mechanism that can operate after being loosed from an encumbered or jammed position.
The present invention provides a borehole tool comprising a tool body having an anchoring mechanism, the anchoring mechanism comprising a) a drive mechanism including a motor, a drive shaft and a clutch mechanism; b) an anchoring arm moveable between first and second positions relative to the tool body; and c) a push rod extending through the clutch mechanism connecting the anchoring arm to the drive mechanism; the push rod engaging a spring which acts to bias the arm into the first position, and driveably connecting the drive mechanism through the clutch such that the arm can be moved between the first and second positions.
In another embodiment, the present invention provides a borehole tool comprising a tool body having an anchoring mechanism comprising a) a drive mechanism including a motor, a drive shaft and a clutch; b) an anchoring arm moveable between first and second positions relative to the tool body; c) a push rod connecting the anchoring arm to the drive mechanism through a link; and d) a spring acting to bias the arm into a first position relative to the tool body; characterised in that the push rod extends through the clutch mechanism and is engaged by the spring to bias the arm into the first position, and is also driven by the drive mechanism through the clutch to move the arm between the first and second positions.
The present invention provides a borehole tool comprising a tool body having an anchoring mechanism comprising a) a drive mechanism including a motor, a drive shaft and a clutch; b) an anchoring arm moveable between first and second positions relative to the tool body; c) a push rod connecting the anchoring arm to the drive mechanism through a link; and d) a spring acting to bias the arm into a first position relative to the tool body; and e) at least one measurement device; characterised in that the push rod extends through the clutch mechanism and is engaged by the spring to bias the arm into the first position, and is also driven by the drive mechanism through the clutch to move the arm between the first and second positions.
In one embodiment, the present invention provides a link for connecting an anchoring arm to a borehole tool comprising at least one hole for affixing a fastener, an orifice for mounting a pivot, a cutout area, and a breakage area.
The invention is applicable to any type of borehole tool that requires the tool body to be urged against the borehole wall. The provision of the push rod extending through the clutch mechanism allows the overall length of the anchoring mechanism to be reduced over that provided by the prior art device.
A ball-bearing clutch can be used which comprises a collar having a number of balls that engage in grooves in the push rod to allow the drive mechanism to move the arm. A spring-loaded retaining ring can be provided to hold the balls in a driving position in the grooves when engaged by the collar.
The drive shaft is typically a drive screw and a nut is used to transmit the driving force to the push rod. Driving force can be applied either through the clutch or by bearing surfaces on the nut which engage directly extensions of the push rod. The two mechanisms can be used to provide reversible drive to the push rod.
The spring can be a coil spring that is located in the tool body around the drive mechanism. Other arrangements of springs or resilient biasing means can be used to urge the arm into the first position.
The anchor arm can be mounted on a pivot on the tool body with the first position being extending away from the tool body and the second position being along the tool body. Thus, the spring can be used to urge the arm away from the tool body and the motor used to provide further drive in this direction for anchoring force, or to provide a counteracting drive to withdraw the arm to the tool body. By reversing the drive to release the clutch, the arm can be held under spring force alone while the tool is moved in the borehole. The pivot can be placed in a link that connects the arm to the drive mechanism, the link having a propensity to fail in a predefined arrangement.
A measurement device can be used to indicate the position of the arm after movement. A measurement device attached to the push rod can be used to measure contact between the anchor arm and the borehole wall. A measurement device can be used to measure the contact force asserted on the borehole wall by the anchor arms. A measurement device can be used to detect forces that indicate the position of the anchor arm. A measurement device can be used to determine the orientation of the tool or borehole wall in a deviated wellbore.